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TROPICAL DEPRESSION FOUR-E DISCUSSION NUMBER 3
NATIONAL WEATHER SERVICE MIAMI FL
2 AM PDT SAT JUL 21 2001
...CORRECTED TO ADD DISSIPATING AT 72 HR FORECAST TIME...
TROPICAL DEPRESSION FOUR-E REMAINS LARGE AND DISORGANIZED WITH A
DIFFICULT TO FIND CENTER. A QUIKSCAT OVERPASS AT 0210Z AND GLIMPSES
OF THE CENTER ON MULTISPECTRAL INFRARED IMAGERY SUGGEST THAT IT
IS STILL ON THE NORTH SIDE OF THE PRIMARY CONVECTION...MEANING
LITTLE CHANGE IN ORGANIZATION. THE INITIAL INTENSITY THUS REMAINS
30 KT.
THE BEST ESTIMATE OF THE INITIAL MOTION IS 310/10. LARGE-SCALE
MODEL ANALYSES INDICATE A WEAKNESS IN THE LOW TO MID-LEVEL RIDGE
TO THE NORTHWEST OF THE CYCLONE...AND THERE ARE FAINT HINTS OF THIS
FEATURE IN WATER VAPOR IMAGERY. LARGE-SCALE GUIDANCE AGREES THAT
THIS WEAKNESS WILL PERSIST THROUGH THE FORECAST PERIOD...BUT MODEL
AGREEMENT ENDS THERE. THE LBAR...BAMD...BAMM...AND NHC91 MOVE
THE CYCLONE NORTHWESTWARD INTO THE WEAKNESS. THE GFDL...THE
UKMET...THE NOGAPS...AND THE AVN ALL CALL FOR A TURN TOWARD THE
WEST-NORTHWEST OR EVEN WEST. GIVEN THE UNCERTAINTY OF WHERE THE
CENTER IS...THERE WILL BE NO MAJOR CHANGES IN THE OFFICIAL FORECAST
AT THIS TIME. THE OFFICIAL FORECAST IS PARALLEL TO AND SLIGHTLY
SOUTH OF THAT OF THE PREVIOUS PACKAGE.
THE DEPRESSION IS MOVING STEADILY INTO COOLER WATER AND THUS IS
RUNNING OUT OF TIME IN WHICH TO STRENGTHEN. THE INTENSITY FORECAST
STILL CALLS FOR THE SYSTEM TO BECOME A TROPICAL STORM IN 12 HR
FOLLOWED BY PEAKING AT 36 HR. BY 72 HR...THE FORECAST TRACK TAKES
THE CYCLONE OVER 22C WATER...WHICH SHOULD CAUSE IT TO START
DISSIPATING. HOWEVER...IF A MORE WESTWARD MOTION DEVELOPS...THE
CYCLONE WOULD STAY OVER SOMEWHAT WARMER WATER AND COULD BE A
LITTLE STRONGER THAN CURRENTLY FORECAST AT 72 HR.
FORECASTER BEVEN
FORECAST POSITIONS AND MAX WINDS
INITIAL 21/0900Z 15.3N 119.1W 30 KTS
12HR VT 21/1800Z 16.2N 120.3W 35 KTS
24HR VT 22/0600Z 17.3N 121.8W 40 KTS
36HR VT 22/1800Z 18.2N 123.2W 45 KTS
48HR VT 23/0600Z 19.0N 124.6W 35 KTS
72HR VT 24/0600Z 20.0N 126.0W 25 KTS...DISSIPATING
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